Data rewritable disc media in which a user can record audio data, such as music, are well known. Such disc media are provided with a data area and managing area within the recordable area. The audio data is pre-recorded in the data area. The disc media is so designed that the managing data for these areas is rewritten every time a recording operation or an erasing operation for audio data is terminated. The managing area is typically referred to as the user TOC (Table of Contents), hereinafter referred to "U-TOC".
An audio recording apparatus is so designed that when an audio recording operation for a musical piece or song takes place a recordable area on a disc is located on the basis of the U-TOC information. The audio recording apparatus then records the audio data for the musical piece on this recordable area. On the other hand, the reproducing apparatus accesses the area in which audio data to be reproduced is recorded to carry out a reproducing operation for the musical piece identified from the U-TOC area.
Generally, for a recordable disc medium such as a magneto-optical (MO) disc or the like, random access recording can more easily be carried out in comparison with tape-type recording medium such as DAT (Digital Audio Tape), a compact cassette tape or the like. Also, it is not necessary to record a musical piece (audio data) on a continuous segment, that is, the program (the audio data for the musical piece) is discontinuously and discretely recorded in plural segments. As used herein, the term "segment" is defined as a track portion on which physically-continuous data is recorded.
Typically, in a system in which data is read out of a magneto-optical disc, this data is temporarily stored into a buffer memory (buffer RAM) at a high-speed rate, and then the data is read out as an audio reproducing signal from the buffer RAM at a low-speed rate to perform demodulation processing. Access between segments enables a reproduced musical piece to be outputted without being interrupted even if the data read-out operation from the magneto-optical disc is temporarily interrupted.
Accordingly, by repeating a recording or reproducing operation between the segments in a high-speed access operation, the recording or reproduction of a musical piece can be performed even when a track for the data of a musical piece is physically divided and separated into plural segments, on the condition that the access operation ends within a data reproducible time due to data accumulation caused by the difference between the write-in and read-out rates of the buffer RAM.
For example, as shown in FIG. 1, it is possible that the first and second audio data (musical songs) are both continuously recorded on a segment T1 and T2, while the fourth and fifth songs are discontinuously recorded on segments T4.sub.(1) -T4.sub.(4) and T5.sub.(1) -T5.sub.(2). FIG. 1 is an illustrative example. In practice, one segment frequently extends over several tracks to several hundreds of tracks.
When the recording, erasing or overwriting operation for musical pieces is repeated for the magneto-optical disc, empty areas are irregularly produced on the tracks due to the difference between play periods of musical pieces to be recorded and play periods of musical pieces to be erased. Through the above discrete recording operation (i.e., when a musical piece is discontinuously and discretely recorded on plural segments), any musical piece which is longer than one recordable segment can be recorded using more than one recordable segment, and thus the data recording area can be effectively used. Audio data to be recorded is not necessarily limited to "musical pieces", and any audio data may be used. In this specification, a block of data (a recording data unit) which has a linked content in combination is representatively defined as a "program" or musical piece.
When the recording operation is carried out for the above type of disc medium, the audio recording operation must be continuously carried out while accessing plural segments serving as recordable areas. When the reproducing operation is carried out, the segments must be accessed in such a manner that a piece of music is accurately and continuously reproduced. In order to satisfy such a requirement, both data for linking the segments allocated to a piece of music, for example, T4.sub.(1) -T4.sub.(4) and data which indicates recordable areas, are stored as U-TOC information. Such information is rewritten as part of every recording, erasing, or overwriting operation as described above, and the recording/reproducing apparatus accesses the U-TOC information and stores it into the memory, for example, at the time when a disc is loaded. Further, when a recording, reproducing, erasing or overwriting operation or the like is carried out, a head access is carried out on the basis of the U-TOC information stored in the memory for the control thereof.
A recording track of the magneto-optical disc comprises continuously-formed clusters CL (1 cluster=36 sectors) each of which includes a subdata area of 4 sectors (one sector=2352 bytes) and a main data area of 32 sectors as shown in FIG. 2. One cluster serves as a minimum unit for the recording operation. One cluster has a length corresponding to two or three circumferences of the track. An address is recorded for every sector. The subdata area of 4 sectors is used for subdata or as a link area, and TOC data, audio data, etc. are recorded in the main data area of 32 sectors.
The sector is further divided into sound groups, and two sectors are divided into 11 sound groups. Data of 512 samples are recorded in a sound group while being separated into L(left) and R(right) channels. One sound group has audio data whose duration is 11.6 msec.
Next, an editing operation of the U-TOC in accordance with the audio recording, erasing, or overwriting operation will be described. FIG. 3 schematically shows the area structure of the disc in its radial direction. For a magneto-optical disc, the area structure is divided into a pre-mastered area and a groove area. The pre-mastered area is recorded with emboss pits which are represented as a pit area in FIG. 3 and a groove area which includes grooves and serves as a so-called magneto-optical area in FIG. 3.
A pre-mastered TOC (hereinafter referred to as "P-TOC") serves to manage information and is repetitively recorded in the pit area. In the P-TOC, the position of the U-TOC is indicated using a U-TOC start address UST.sub.A, and, further, a read-out start address ROA, a start address of recordable user area RST.sub.A, a power cal (calibration) area start address PC.sub.A are also indicated.
The groove area is formed subsequently to the pit area at the innermost peripheral side of the disc. Within the groove area, an area extending to the address which is indicated as the read-out start address RO.sub.A in the P-TOC is used as a recordable area, and subsequently is used as a read-out area.
A recordable user area of the recordable area, in which data is actually recorded, extends from the position (address A.sub.MIN) indicated as a recordable user area start address RST.sub.A to the position (address A.sub.MAX) just before the read-out start address RO.sub.A. An area located before the recordable user area start address RST.sub.A in the group area is used as a managing area for recording and reproducing operations, and the U-TOC as described above, etc. are recorded in this area. An area whose length corresponds to one cluster is provided as a laser power calibration area from the position indicated as the power cal area start address PC.sub.A.
The U-TOC is recorded at a predetermined position in the managing area for the recording or reproducing operations over three successive clusters, and the address position at which the U-TOC is recorded is indicated by the U-TOC start address UST.sub.A. The U-TOC is provided with information on the recording status of the recordable user area as managing information.
Now, it is assumed that four pieces of music or audio data M.sub.1 to M.sub.4 are recorded in the recordable user area as shown in FIG. 3. That is, first audio data M.sub.1 is recorded on segments having addresses A.sub.1 (=A.sub.MIN) to A.sub.2, second music data M.sub.2 is divided into a portion M.sub.2(1) which is recorded on segments having addresses A.sub.3 to A.sub.4, and a portion M.sub.2(2) which is recorded on segments having addresses A.sub.11 to A.sub.12. A third musical piece M.sub.3 is recorded on segments having addresses A.sub.5 to A.sub.6, and a fourth musical piece M.sub.4 is recorded so that it is divided into a portion M.sub.4(1) recorded on segments having addresses A.sub.9 to A.sub.10, and a portion M.sub.4(2) recorded on segments having addresses A.sub.13 to A.sub.14.
In this state, segments F.sub.(1) having addresses A.sub.7 to A.sub.8, and segment F.sub.(2) having addresses A.sub.15 to A.sub.16 (=A.sub.MAX) are allocated to recordable areas on which no music data has been yet recorded, that is, recordable free areas.
This state (area structure) is managed as shown in FIG. 4 in the U-TOC. The U-TOC is provided with a corresponding table indicating data portion which includes various kinds of table pointers (P-DFA, P-EMPTY, P-FRA, P-TNO1 to P-TNO255) as shown in FIG. 4, and also with a managing table portion having 255 part tables (01h) to (FFh) in correspondence with the corresponding table indicating data portion. The numerical value affixed with an "h" are represented by hexadecimal notation. Each part table contains a start address, an end address, a track mode for one segment on the disc, and link information for linking the part table to another part table. In this construction, each part table is indicated by each kind of table pointer of the corresponding table indicating the data portion to thereby manage the segments.
The table pointer P-DFA indicates a defective area on the disc. Now, assuming that no defect exists in the recordable user area as shown in FIG. 3, the table pointer P-DFA is set to "00h". The table pointer P-EMPTY indicates an unused part table.
The table pointer P-FRA is used to manage free areas as recordable areas and, in the case of FIG. 4, the table pointer P-FRA indicates a part table (01h). Actually, each table pointer indicates a part table with a numerical value with which the address for the part table is determined through predetermined calculation processing.
Information in the free area F.sub.(1) (as shown in FIG. 3) is indicated in the part table (01h). That is, the addresses A.sub.7 and A.sub.8 are indicated as a start address and an end address, respectively. Further, since another segment serving as the free area F.sub.(2) exists, a part table (09h) is indicated by link information of the part table (01h). In practice, a numerical value with which the address for a part table is determined through predetermined calculation processing is indicated as link information.
In correspondence with the free area F.sub.(2), the addresses A.sub.15 and A.sub.16 are indicated as a start address and an end address respectively in the part table (09h). Since no further segment serving as a free area exists, this part table (09h) is not required to be linked to another part table, and thus the link information thereof is set to "00h".
Through the management of the free area as described above, the address for any segment serving as a free area can be obtained by searching part tables with the table pointer P-FRA being set to a starting point, and the music data or the like can be recorded on the segment serving as the free area. Music data which has already been recorded is managed in the same manner as described above. With respect to the musical pieces (music data), 255 musical pieces maximum can be managed by the table pointers P-TNO1 to P-TNO255.
With respect to the first musical piece M.sub.1 for example, the start address A.sub.1 and the end address A.sub.2 therefor are indicated in a part table (02h) which is indicated by the table pointer P-TNO1 (02h). Since the musical piece M.sub.1 is recorded on one segment, the link information of the part table (02h) is set to "00h".
Further, with respect to the second musical piece M.sub.2, the start address A.sub.3 and the end address A.sub.4 therefor are indicated in a part table (04h) which is indicated by the table pointer P-TNO2. In this case, the musical piece M.sub.2 is discontinuously recorded on two segments, and thus the addresses A.sub.3 and A.sub.4 indicate only one segment for the first half (M.sub.2(1)) of the musical piece M.sub.2. Accordingly, in this case, a part table (06h) indicates the link information for the part table (04h), and the start address A.sub.11 and the end address A.sub.12 are recorded in the part table (06h) to indicate the other segment for the second half (M.sub.2(2)). No further linkage is required for this musical piece, and thus the link information of the part table (06h) is set to "00h".
With respect to the third and fourth musical pieces M.sub.3 and M.sub.4, the positions of segments for these musical pieces are managed by those part tables which are obtained from the table pointers P-TNO3 and P-TNO4 serving as the respective starting points. In this case, since only four musical pieces are recorded, the table pointers P-TNO5 to P-TNO255 are not used and thus set to "00h".
The segment position of each musical piece is managed in the manner as described above, and thus the reproducing operation can be properly performed even when plural musical pieces are required to be reproduced in an irregular order or when each of the musical pieces are discontinuously recorded in two or more segments.
As described above, the table pointer P-EMPTY indicates an unused part table. In this case of FIG. 4, the table pointer P-EMPTY indicates a part table (08h). On the basis of the link information of the part table (08h), unused part tables which are linked to one another until an unused part table (FFh) serving as the last part table are managed by the link information. These unused part tables are subjected to the link management as shown in FIG. 4. The link information of the part table which is the last part table for the linked unused part tables, in this case, the part table (FFh), is set to "00h" to indicate no further linkage.
In the course of the recording/erasing operation of musical pieces or the like for this type of disc medium, wasted areas (trash areas), which are not managed by the U-TOC having the managing mode as described above, can occur. These trash areas are caused in the following ways. In order to prevent music data on another audio track from being erroneously erased when a piece of music (music data) is recorded, a guard band area whose length corresponds to several clusters may be provided before and after the music data. The sound-recording start position may be defined on the assumption that the sound recording is carried out on a cluster basis. The music editing involving partial erasure or synthesis of a musical piece (music data) may be carried out.
For example, in the case of FIG. 3, shaded portions between addresses A.sub.4 to A.sub.5, addresses A.sub.6 to A.sub.7 and addresses A.sub.12 to A.sub.13 are considered segments or addresses for trash areas which do not appear in the managing mode of the U-TOC as shown in FIG. 4. The occurrence of these trash areas causes a reduction in the recording capacity of the disc and expenditure of space in the part table. In order to solve this problem, it has been conventionally adopted that the U-TOC is re-edited at a prescribed time to reduce the trash areas. The editing processing of the U-TOC is executed, for example when music data is erased, or the re-editing of the U-TOC is instructed by an user's manipulation, or the control device determines an increase of trash areas.
The editing processing in accordance with the erasing operation will be described. It is assumed that the music data M.sub.3 in the state of FIG. 3 is erased, as shown in FIG. 5. In this case, the segment of the music data M.sub.3 is newly installed in a free area, and at the same time trash areas, as indicated by the shaded areas, located before and after the segment of music data M.sub.3 are also created in the free area. Here, by combining the free area F.sub.(1) at the subsequent addresses A.sub.7 to A.sub.8 with the above free area, a new free area F.sub.(1) at addresses A.sub.17 to A.sub.18 can be formed, so that the trash areas at the addresses A.sub.4 to A.sub.5 and the addresses A.sub.6 to A.sub.7 can be erased. That is, the U-TOC may be rewritten so that the recordable user area can be newly managed by the U-TOC in the state of FIG. 6.
Accordingly, in such a recording apparatus, the state shown in FIG. 4 is rewritten to the state shown in FIG. 7 on the basis of the U-TOC information stored in the memory. The portions as indicated by oblique lines in FIG. 7 correspond to portions rewritten from the state of FIG. 4.
That is, the start address of the part table (01h) representing a free area F.sub.(1) is rewritten to the address A.sub.17, and the music data M.sub.4 is newly set as the music data M.sub.3 because the previous music data M.sub.3 has been erased. The data written in the table pointer P-TNO4 (that is, data indicating a part table (07h)) is written in the table pointer P-TNO3, and the table pointer P-TNO4 is set to "00h". Further, since the part table (03h) which previously indicated the segment for the music data M.sub.3 is currently unused, it is linked subsequently to the part table (FFh) with the table pointer P-EMPTY set at a starting point, and it is managed as an unused part table. Through the editing of the U-TOC as shown in FIG. 7, the state of FIG. 6 can be realized.
In order to perform the above editing, the part tables in the U-TOC are required to be searched to judge whether adjacent segments before and after the segment of the recorded music data M.sub.3 are located in an area in which music data is recorded or a free area in which no music data is recorded. In addition, it must be judged whether any trash area exists between the segment of the music data and the segments before and after the music data segment.
As is apparent from FIG. 4, any part table for a segment which is actually adjacent to a segment indicated by a part table on the disc cannot be identified from the part tables, and thus the following searching operation must be carried out. That is, the addresses of segments of all part tables are successively read in while compared with the address of a reference segment (segment of the erased music data M.sub.3 in this case), and the segment having the nearest address is determined to be an adjacent segment.
Usually, this type of recording apparatus is provided with a memory controller for carrying out an output operation of memory write-in/read-out addresses and a stored data receiving operation for a memory for storing the U-TOC. A system controller (microcomputer) controls the memory controller to execute storage/read-out for data. The system controller reads in the U-TOC from the memory to control the actual recording operation, etc., and also carries out the editing operation of the U-TOC as described above. In order to perform the editing operation, the system controller carries out the searching operation for all the part tables through the memory controller as described above, and also carries out an address comparing operation for each searched part table to search adjacent segments.
Therefore, it takes a long time to perform data communication of the part tables from the memory (memory controller) to the system controller, and the communicating and comparing processing as described above imposes a significantly larger load on the system processing.
Particularly in a case where data reception and transmission between the memory controller and the system controller is carried out through serial communication, for example, when the processing for trash areas as described above is executed for the editing operation, the processing time requires two minutes at maximum, and this requirement for the processing time is unfavorable for practical use of the recording apparatus.